I propose to study binocular interaction at the level of single neurons in the second tier of the cat visual cortex, area 18. My experiments should help establish a new version of the fusional theory of stereopsis in terms of single unit responses. My first series of recordings is designed to test the notion that facilitation is involved in forming binocular-only responses in a class of area 18 neurons, and that inhibition is involved in sharpening the range over which facilitation occurs. After becoming familiar with the binocular responses of adult area 18 neurons, I propose to study the normal development of those responses in kittens. Anatomical observations suggest that area 18 may develop later than 17. As the experiments on normal development proceed, I want to study the effects of artificial strabismus on the development of binocularity in area 18. I feel that a reversible strabismus can be perfected, and with it the possibility of recovery from strabismus can be studied. Finally, I wish to pursue the idea that proprioceptive signals from the extraocular muscles can influence single unit binocularity, especially if such signals are chronically imbalanced. If this idea is correct, proprioception may be implicated in the loss of stereopsis which follows uncorrected stabismus in human development.